I just bought a slim (corona made august 22nd 2011 though it was a new purchase from the store) and I'm really happy with how quiet it is compared to my old one I sold 3 years ago. That is, until I try to play a game.

some games I can hear the drive reading in those short bursts and a lil louder on the fan but nothing worse than a wii or ps3 slim. some games however... it whirs loudly and the fan seems to be louder too (like my old xbox but the drive itself is louder than that) it's such a large difference that I can easilly tell when it stops even when not paying attention as all noise in the room just vanishes.

how loud is normal for these things? is it normal to have it louder for some games only? anything i can do to troubleshoot before calling microsoft?

it's most likely due to those games having a lot of tiny files. I'd suggest ripping those games to ur hdd. the drive will only start up for a split second to verify the disc and files then it should be relatively quiet.